1. Field of the Invention
This invention relates to improvements in a wiper system for wiping a windshield or window glass, and more particularly to such a wiper system in which the wiper blade moving characteristics is changeably controlled in the going and/or returning strokes of one cycle of wiper blade movement.
2. Description of the Prior Art
Hitherto a variety of wiper systems have been proposed and put into practical use. A typical one of them is shown in FIGS. 1A and 1B of the drawings of the present application. In FIG. 1A, a conventional wiper system includes a wiper blade 2', 2A' which is in contact with the surface of a windshield or window glass 1' and movably attached to a wiper arm 3', 3A' which is driven by a wiper motor 4'. More specifically, a crank 6' is connected to a rotational or drive shaft 5' of the wiper motor 4'. The crank 6' is connected through a link 7' with a lever 8' on which the wiper arm 3' is fixed. The link 7' is further connected through a link 9' with a lever 8A' on which the a wiper arm 3A' is fixed.
As shown in FIG. 1B, when the crank 6' makes its half rotation along points P.sub.1 ', P.sub.2 ' and P.sub.3 ', the lever 8' swingingly moves a predetermined angle passing through an initiation position S.sub.1, an intermediate position S.sub.2 and a termination position S.sub.3 under the action of the link 7'. In accordance with this movement of the lever 8', the wiper blade 2' makes its going stroke upon contacting with the surface of the windshield 1'. Subsequently, when the crank 6' makes its further half rotation along points P.sub.3 ', P.sub.4 ' and P.sub.5 ', the lever 8' swingably moves passing through the initiation position S.sub.3 and an intermediate position S.sub.4 to be restored to a termination point S.sub.5. Thus, the wiper blade 2' makes its returning stroke, thereby completing one cycle of wiper blade movement or wiping the windshield. In this one cycle of the wiper blade movement, the displacement of the link 7' changes as shown in FIG. 1C, while the moving speed of the wiper blade 2', 2A' changes as shown in FIG. 1D in which the moving speed change is represented as a mere sine wave. In other words, the wiper blade moving or wiping characteristics of the conventional wiper system is such that the wiper blade moving speed gradually accelerated at a first half period and decelerated at a latter half period in each of the going and returning strokes of the wiper blade 2', 2A'.
However, difficulties have been encountered in the above conventional wiper system. That is, during wiping operation of the conventional wiper system whose wiper blade moving speed changes like a sine wave, the moving speed of the wiper blade is observed and felt approximately constant. Such moving speed characteristics is less in change, and therefore the driver feels it troublesome or bothersome, thereby increasing the feeling of fatigue or exhaustion of the driver. In addition, it is a recent trend that the area of window glasses is widened. In this regard, it has been required to reduce the feeling of troublesomeness due to the moving characteristics of the wiper blade of the wiper system.
Techniques of variable control of the wiper blade moving characteristics have been proposed and are disclosed in Japanese Patent Provisional Publication Nos. 62-198549 and 61-139542. However, even such techniques fail to improve the troublesomenss of movement of wiper blade.